The disclosure relates generally to valves having means for relief of internal cavity pressure. More particular, the disclosure relates to a bi-directional valve having means for cavity pressure relief integral to its body.
Ball valves are used extensively to control fluid flow through piping systems because they are reliable and can withstand high pressures and temperatures. Each ball valve typically has a body with a passage extending therethrough. The valve is coupled between adjacent sections of a piping system such that the through passage is aligned with the flowbores of the pipe sections. The valve further includes a ball disposed within the through passage. The ball has a bore extending therethrough and is rotatable relative to the valve body. When the ball is rotated to align the ball bore with the body through passage, the valve is open, and fluid in the upstream pipe section may pass through the valve to the downstream pipe section. When the ball is rotated such that the ball bore and the body through passage are perpendicular to one another, the valve is closed, and fluid is prevented from passing through the valve.
When the valve is actuated to move from the open position to the closed position, the ball bore forms an enclosed cavity with fluid entrapped therein. In the event that the temperature surrounding the valve increases, the temperature of fluid within the valve cavity also increases. This, in turn, causes the pressure of that fluid to increase, sometimes to a level beyond the valve pressure rating. Excessive fluid pressure within the valve can result in damage to and/or failure of the valve.
To alleviate this potential problem, the valve may further include means for venting pressure buildup within the valve cavity. For instance, many ball valves include self-relieving seats, which displace and/or deform to create a leak path when pressure within the cavity exceeds a certain level. In practice, however, the level at which the seats relieve may vary from one valve to the next. Consequently, the pressure relieving ability of these valves is inconsistent and unreliable. Moreover, the seats are subject to fatigue damage due to repeated venting and temperature changes. When damaged, the seats may allow leakage through the valve.
Other ball valves may include an add-on device, such as a spring-loaded piston, external to the valve body with a pressure relief tap extending from the device through the valve body to the cavity. When the cavity pressure is sufficient to overcome the spring force, the piston displaces, and the cavity pressure is relieved. Over time, the pressure relief tap can become a leakage path from the valve to the atmosphere.
Embodiments of the present invention are directed to valves with means for cavity pressure relief that seek to overcome these and other limitations of the prior art.